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Why do ATC instructions to change level include the words "climb" or "descend"?
ATC instructions to change level include the words "climb" or "descend" depending on the direction of the vertical maneuver. For example, "Descend to 2500 feet" or "Climb to FL70".
For comparison, instructions to turn to a specific heading often, but not always, include the words "right" or "left". We can say "Turn right heading 120" or "Turn left heading 360", but in some situations we may simply say "Fly heading 180". When using "Fly heading", it is implied that the turn should made in the direction that requires the smallest change of direction. A pilot heading east instructed to "Fly heading 360" will always perform a left turn, even if the word "left" was not included in the original instruction.
Similarly, for speed control, we have phrases such as "Reduce speed to 220 knots" and "Increase speed to 280 knots", while we can also simply use "Maintain 240 knots", in which case the pilot will then speed up or slow down as appropriate.
Radio phraseology is designed to be as short as possible, and radio calls should include no excessive words. This makes me wonder, why do we always include "Climb" or "Descend" in level instructions? If a flight is at FL320 and we need to instruct it to get up to FL340, it is self-evident that the pilot must climb, not descend. Using this logic, a phrase such as "Maintain FL340" or even just "FL340" (Example: "[callsign], FL340") should suffice.
I can think of reasons who we do use climb and descend. It most likely improves situational awareness for both controllers and pilots (including other flights on the frequency). It could also enable pilots to identify situations where they mishear a level instruction (Example: for a flight on FL320, instructed to "Maintain FL240", the crew might mishear this and think they are cleared to FL340. If the phrase "Descend to FL240" is used, this is less likely to happen). Finally, "Climb to" and "Descend to" is not much longer than "Maintain".
However, this leaves the question of why we have such "neutral" phrases for heading and speed restrictions. Wouldn't enforcing the use of "Right", "Left", "Increase" and "Reduce" introduce the same benefits we get from using "Climb" and "Descend"?
Is there a historical reason the phraseology concerning level changes is designed the way it is - perhaps an incident or accident where another phraseology was used? Or is it a coincidence that level instructions are different compared to heading or speed restrictions?
I can come up with "qualified guesses" myself, so I am hoping someone with actual knowledge on the topic can provide a factual answer.

For me it would seem odd to exclude it, like "N1234, maintain 3500". As a pilot when I hear a controller say *"N1234 Climb 3500" I can do two things, first mentally prepare for an instruction to maintain an altitude higher than my current altitude, and second, verify that the controller knows where I am. If the controller were to say "Climb 3500" and I'm at 5000, I would ask for clarification because either I heard the call wrong, or the controller isn't talking to who he thinks he is.

Because of wind, ATC will know your track but may not know your specific heading. If ATC has given a heading to another airplane and wants to make sure your paths don’t cross, they may give you a heading that keeps you along a parallel track. The heading may be right, left, or the same as your current heading. Often, they will ask you for your heading first, and then give you a new one or tell you to maintain the present heading.

ATC will frequently tell me to turn 20° right or left for traffic. They don’t care what my heading is now and what it will be after I turn, they just want me  out of the way, and based on my track, 20° looks like it should do it.

What's the alternative? "Maintain FL340" has the same number of syllables as "Climb to FL340" but less clear. Every instruction needs an imperative verb: Climb, Descend, Maintain, and Expect seem pretty concise.

Poorly adjusted background noise suppression can delete the or corrupt start of a message. If "two five hundred feet" was transmitted it might be received as "five hundred feet". If "Climb to .... " is transmitted, losing the first word is less dangerous.

related: https://aviation.stackexchange.com/questions/102332/why-are-we-still-using-audio-to-communicate-between-atc-and-pilot

Adding the instruction "climb/descend" to the flight level is an example of linguistic redundancy offering a very rudimentary form of error detection for voice communication (which is inherently "unreliable", as it can be misheard by the receiver – on top of the sometimes poor ATC radio channel quality):

In […] telecommunication, error detection [is a] technique that
  enables reliable delivery of […] data over unreliable communication
  channels. Many communication channels are subject to channel noise,
  and thus errors may be introduced during transmission from the source
  to a receiver. Error detection techniques allow detecting such errors.
  (source)

Therefore adding the instruction "climb/descend" offers an additional layer of security, because

the pilot would never descend when instructed to climb (and vice versa)
and the pilot is able to detect an instruction mismatching the flight level, i.e. "climb to FL240" when already at FL320 (taking the example in your question)

... but not perfect security (because the pilot at FL320 would not detect an error if ATC mistakenly instructs him to "climb to FL420" instead of "climb do FL400"). Therefore ATC instructions are repeated on the receiving end by the pilot.
(For a non-aviation analogy, the same technique is applied when dates are agreed upon on the phone as "Friday, 4 January 2019", although the day of the week is already implied by the date itself.)
In essence, your question "Why do ATC instructions to change level include the words 'climb' or 'descend'?" can be best answered by the (limited) added information transmission security these instructions provide. Therefore for me the real question is why instructions concerning speed and heading don't obligatorily require this sort of disambiguating instruction – especially so as this unspecificity can demonstrably lead to confusion. I hope someone else will be able to answer this part of your question, as I don't have specific knowledge about this aspect of it.

There are a lot more ways to let an aircraft climb or descend than giving just a simple descend or climb instruction and all these additional instructions base off the basic instruction to climb, e.g.
R: DLH123, descend FL120
R: DLH123, descend FL120, cross ABCDE at or below FL150
R: DLH123, descend via ENTRY1A arrival
R: DLH123, when ready descend FL120 to reach at ABCDE

Please note that the phraseology to descend or climb does not include the word to, so it doesn't make it any longer than maintain.
Additionally, just saying
R: DLH123, FL120

is too ambiguous and could lead to misunderstandings, as any level or altitude transmission over the frequency without an instructing word is interpreted as a statement. Reading the above would be interpreted as DLH123 giving their current flight level, rather than an action item.

Actually, the word 'to' is mandatory to use, check doc 9432. Good answer regardless.

In the US, 7110 does not include the word "to" in any acceptable phraseology for altitude assignments or changes to assignments. In the ATC classes I took (I'm not a controller, just took some classes while seeking my aviation degree), we were specifically told to never use the word "to" during any altitude assignments.  I also thought I remember the words "to" and "from" being removed from ICAO phraseology, but I cannot find that source.

Consider these instructions: "descend to seven thousand?" or "descend two seven thousand?"    quite the difference. (which is we don't hear to in instructions much)

Communicating the supplementary word left/right wrongly still describes a possible action that may not end up well.
Communicating climb/descent incorrectly does not, and may help to detect that the altitude inside the message has been misunderstood.

Sometimes ATC reallly does want a wrong-side turn, e.g. for spacing. And some controllers seem to give the direction on every turn, regardless of whether it is right or wrong side. I've noticed they tend to say the direction twice when it is wrong side, probably to be sure the pilots don't miss it.


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What is the purpose of logo lights on airliners?
Why do modern airliners use lights to illuminate the sides of their tails and illuminate the airline's logo?  Is this just done to give ground and tower controllers an easy way to differentiate between multiple jets on the ground during night ops or direct them to the appropriate gates e.g. Delta flights to Delta terminal, Qantas flight to Qantas gates, etc.?

I don't think it is a duplicate. This question is specifically about why we have logo lights on the vertical stabilizer, not when to turn them on.

@kevin the why part is also included in the question, as well as some of the answers.

Trivia:  Airplanes didn't have Tail/Logo lights until Hugh Hefner put tail lights on the Bunny Logo of the Playboy jet.  The idea caught on quickly, and many others copied it, including Donald Trump.   Now most planes have logo/tail lights.

There are multiple reasons.

First of all: Of course promotion for the airline.
Another reason is the visibility. Airliners have several lights and strobes (Nav lights, rotating beacon, ...) but this can be overseen. The logo light is used to see if there are any other aircraft crossing the taxiway or apron. It's just better to have a big, bright illuminated area, instead of a few small lights.
And ATC has also something to do with it. Many phrases regarding taxiing include airline names. For example:

AFA739, give way to an Air Berlin A320 moving from left to right on taxiway Bravo

ATC and the pilot can visually identify the companies name thanks to the logo lights.

I can think of a couple of reasons:

To allow ATC to identify an aircraft's livery
To promote the airline
To illuminate the end of the aircraft's body, so it is easier to determine, e.g. if the whole body section has crossed the runway threshold.

source: Stack Exchange

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What is the criteria for determining whether an airport will be towered or uncontrolled?
I thought about this in reference to the question about Schamburg Airport in Chicago.  Is there a particular criteria for an airport, for instance the amount of instrument traffic going into and out of an airport, high density flight operations, etc., which would require the FAA to classify an airport as a controlled environment and surrounded by controlled airspace (Class D, C, or B) all the way to the surface?
I guess by question is targeted at what is the threshold between where the FAA will require an airport to be controlled and where it is allowed to be uncontrolled yet allows for reasonable and safe flight operations in the National Aerospace System.  I understand the basic differences between Class D, C, and B airspace designations, but I want to know if that is regularly evaluated and assigned new airspace designations surrounding the airport and control requirements.

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What exactly is this thing at LAX?
I noticed this recently on Google Earth located on the southwest corner of KLAX in Playa Del Ray, CA.

Upon examination, I'm guessing the facility is used by firefighting crews for practice putting out jet fuel fires on an aircraft on the ground.  I'd also venture a guess that the smaller fuselages to the right are probably used by the LAPD SWAT team, federal sky marshals or other LE organizations for doing anti-hijacking and other anti-terrorism training.
But what's with all the taxiway paint markings around the red fire aircraft?  Do airport paint crews go out there to test their equipment?

"smaller fuselages to the right are probably used by the LAPD SWAT team, federal sky marshals or other LE organizations for doing anti-hijacking and other anti-terrorism training" I believe they are used more for crew evacuation training.

"Do airport paint crews go out there to test their equipment?" - You know when you change the ink in your printer and print a page to check the ink's flowing properly? Pretty much that

That's what I was thinking


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What are the differences between FCLP markings and equipment and the LA on a ship?
Most Naval and Marine Corps Air Stations have these markings on at least one or more of their runways:

It’s a Field Carrier Landing Practice (FCLP) area and used to maintain proficiency amongst carrier based fixed wing squadrons with landing in a carrier.
The area is marked like the Landing Area (LA) on a carrier.  However, since the real carrier is steaming forward at 25-30 kts during recoveries, the perception of the pilot approaching the real LA will be a little different than when approaching the FCLP area.
Approaching a carrier with an LA angled 9° left of the ship’s keel axis requires not only that the pilot crab to the right on approach but the closure with the touchdown area, when at optimal AoA will be 25-30kts slower at the boat than when doing FCLP approaches.
I’m wondering if the Navy has modified these FCLP area making them elongated, decreasing the glideslope angle in the IFLOLS, etc. to more realistically simulate an approach to a carrier during FCLP workouts.

Not really any different than adjusting for changing winds at the local airport, though the range of variability is different.  I'd think the pitching motion of the deck would have a bigger impact. I can't think of an easy way to simulate that.

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What are the procedures for flying supersonic over international waters?
Supposing I owned a supersonic aircraft eg a MiG-21 and wanted to fly the jet out into international waters for a supersonic speed run.  Are there any particular ATC procedures for doing so?

here's hoping you're considering buying one of the ones that keeps going on sale.  I think the one at EFD is still available and really needs some TLC

In the US?  You'd be talking to ATC to clear the ADIZ around the US coast. Then keep talking to them to make sure you aren't going to fly into any slower transoceanic traffic.  And then to get clearance back into US controlled airspace.

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Mechanical vs Pneumatic Stall Warning Systems
Light Cessna aircraft - at least the high wing single engine line - have commonly made use of a solid state pneumatic stall warning system.  The system is fairly unique to Cessna airplanes and makes use of the fact that negative pressures form over the leading edge of the wing near the critical angle of attack, causing a reverse flow of air through the warning system and causing a horn in the cockpit to sound.  Most other light aircraft make use of a movable tab with activates an electric switch when depressed by airflow near the critical AoA, causing a chime, horn or other aural cue in the cockpit alerting the pilot to an impending stall.  Here's the question:  What are the pros and cons of each of these systems?  From brainstorming, I can come up with the following:
Pneumatic Stall Warning Systems:
Pros:

Solid State; has no moving parts which can break or become immobilized or altered by neglect, damage or airframe icing.
Does not require electrical or other sources of power from engine or elsewhere to work.

Cons:

Orifice can become blocked by FOD or airframe icing, causing the system to become inoperative.

Mechanical Stall Warning Systems:
Pros:

Simple operating and mature technology.
Can be electrically heated to prevent immobilization by airframe icing, though this is not always the case depending on the aircraft.

Cons:

Moving parts which can break.
Tab can be bent by maintenance or neglect, causing system to operate erroneously and give false readings.
Can be immobilized by airframe icing, rendering the system inoperative.

Can anybody think of other pros and cons for each of these systems?

Pneumatic one can also be heated, perhaps even easier. (Though I've never seen it done).

Electromechanical:
Pro - can be tested easily during preflight by turning the mains on and manually actuating the tab
Pro - Potentially lighter (although not my much)
Pro - easy to install multiple switches in parallel if you want to trigger based on a stall of differing characteristics as is done on the Piper Seneca
Pro - Easy to wire into other systems. Maybe you want to add a stick shaker or some kind of feed back to the autopilot, much easier if its already generating an electrical signal.
Pneumatic:
Con - can only be tested by creating a low pressure on the horn, not as easy as the tab option
Many of the above pros become Cons for solid state units, like being harder to connect to other systems with out a transducer, harder to add multiple units without multiple horns, and the weight.

I doubt the electromechanical one is lighter, even potentially, if you consider all the wiring required.

Cons for pneumatic systems from a maintenance perspective also include decoupling of pneumatic tubing and mechanical failure of the horn reed.

One pro of the pneumatic one not yet mentioned is that it is somewhat 'analog'. It's not just on/off; it starts faintly and intermittently and then raises to a solid loud signal as the AoA increases. This gives a somewhat better picture of what's happening, esp. on landing. Perhaps even prevents the pilot from freaking out when it happens unexpectedly.

Some modern electronic stall indicators will give a similar indication via intermittent, increasing, then finally continuous tones as AoA approaches critical.  These are somewhat more complex than the basic on/off tab based stall warning as they sense differential air pressure (dual port pitot), but far more useful for the same reasons you state above.

Main problem with the Cessna one is all you get is that whistle.  When I've flown Cessnas in the past I never paid much attention to it as it just blends in with other sounds like whistles coming from flaps or a door that leaks ("That funny whistle is the stall warning? Really?").  Not as effective as the BLAAAAAAAAAAAAAAAAAAAAAAAA coming from an electric one.

I have no trouble hearing the pheumatic horn, even with active noise cancelling headsets. I've not noticed any whistles from flaps, that's a new one. Door seals,  that's maybe more of a whooshing sound. Guess it can vary from airplane to airplane.

I've flown good number of different types of airplanes, and they can make all kinds of noises especially when they're old and beat up lol.

My experience is again the opposite... Never had a problem hearing the horn, it's so distinctive and very unlike any other sound potentially emitted by the avionics. I posted a separate answer explaining some specifics.


text:
What does Hawaii ATC do in the case of ICBM warnings?
Recently somebody pushed the wrong button when testing the ICBM warning system in Hawaii and set off an ICBM warning statewide for 45 minutes.

In all probability ATC would ground departing flights and possibly local ones, but what about inbound flights? Were they ordered to turn back? Continued inbound? What is the procedure for dealing with such a warning?

Why ground departing flights? The survival of the passengers would be better served by getting them in the air and as far away as possible.

@GdD Who's to say it will get far enough away from any possible EMP? The warning suggested that people "find shelter immediately". Maybe if the aircraft was taxiing out, but not anything still in the process of boarding.

It's an interesting question that I'm hoping gets some good answers @RonBeyer.

Related, maybe duplicate: What level of information does a PIC have about a missile crossing their aircraft route?

@mins Related, yes, although the answer to your question is more about NOTAM's about known launches, and doesn't really address what ATC does in an emergency (unknown launch, limited reaction time, etc).

Here's an account that NATCA shared on their facebook page:

Veteran Honolulu Control Facility (HCF) member Steve Olson, recounting the experience of working yesterday:
“8:07am I was plugged in working airplanes like I do every Saturday morning, when the day took a turn into the surreal. Pilot after pilot started to check in with the same question. ‘Center, can you confirm the missile launch?’
“Then, as questions on the control floor were asked, it seemed like every phone in the room started ringing. The word ‘confirmed’ stung like a knife in the gut. As I started to advise the pilots on frequency that the missile launch is confirmed, the frequencies grew silent.
“As I did the only thing I could, continue to take care of the planes in my charge, all I could do was think about the ones I love, my loving wife and amazing kids. With less then 10 minutes there was nothing I could do.
“We found out rather quickly that it was a false alarm, but it seemed like forever.
“With my heart racing and my stomach in my throat, this is what was in my mind. Every day, for the last 29 years, when I leave home for work I hug Meagan, kiss her and tell her I love her. It may sound silly and trite, but today, for 10 long minutes, it mattered.
“Don’t take anything or anyone for granted.”

While a good account of what happened, it doesn't really say what was done, just that they "took care of the planes in my charge". I wonder if that meant getting them on the ground, turning some around, etc.


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Will the new airmen certification standards make it more difficult to add ratings?
As of June 15, 2016, the FAA has changed from PTS/Knowledge tests to the Airmen Certification Standards which is a relatively significant paradigm shift in how airmen are certified.
The underlying reason to move to the ACS was to evolve the outdated PTS (practical test standards) and to align airmen certification towards risk management and the existing national airspace system.
The question I have though is for people who have earned their certificates under the old PTS system and would like to add a rating like an Instrument rating, or another certification like commercial.
Will the new ACS make it more difficult for existing pilots to add ratings? I'd like to know from the standpoint of part 141 and part 91 training centers.
One of the reasons I ask is I went up with my CFI last week and went into some slow flight. I set up to bring the aircraft into the stall buffet and fly it a few knots above stall speed but he said that the new ACS said that the stall horn cannot sound during slow flight, which seems counter intuitive to me. The point of slow flight is to know how to handle the aircraft at or near stall. There is a lot of handling difference between VS0 and VS0+20kts.
So that got me thinking, what would I have to relearn in pursuit of an instrument rating that would make it harder that I probably wouldn't have to under the old PTS?

I took my instrument rating airplane knowledge test today. I had never seen anything like a good many of the questions and I've gone through many practice tests and over 500 pages of questions from the test bank. I passed but it seemed harder to me than any of the practice tests I took. (ACS went into effect less then two weeks ago but I don't know how it has affected the written tests)

I think it's tough to answer this. Asking about specific differences between PTS and ACS tasks or criteria is clear, but asking if something is now more difficult seems very subjective. For example, in your stalling scenarios the ACS isn't any more difficult as such, it's just different. I understand that might be annoying for someone about to take a checkride, but I don't know if there's really a question there. Perhaps if you focus on identifying differences between the PTS and ACS you might get a better response.

Not significantly. The fundamentals of evaluation have not changed, and certainly the fundamentals of your next rating haven't changed. A few of the specific tasks have changed between PTS and ACS, like the point you raise. And, yes, you will need to review the ACS or PTS (whichever is in effect for your next rating -- not all have transitioned) in detail, so that you're aware of what's expected of you.
The major parts of any checkride will be your basic knowledge of the subject, your ability to move the aircraft through the air to standard, your ability to demonstrate sound judgment including a thorough evaluation of pre-flight risks and your overall attitude toward flying. That really hasn't changed with the ACS. The regulations have not changed either. The ACS is meant to give instructors and examiners a more holistic approach to evaluate the above factors.

authors: Сергей Чалов


text:
What qualifies as a major overhaul?
I have an engine that took a prop strike (previous owner).  The engine was completely disassembled to check the crank, case, etc for damage.  It was reassembled with new parts, bearings, rings, etc., overhauled cylinders, and mags with fresh 500 hour inspection. The logbook entry says "0 SMOH Lower End."  What else would be required to list this engine as simply "0 SMOH?"  How should I track this in my log book?

Which regulations are you asking about?   FAA, EASA, etc.?

This is close to being a dupe of this question

It's probably not possible to get a caveat-free zero since major if any time has been logged since the log entry.  You're tracking two numbers now:

Time since bottom
Time since top (if a top was done, maybe cyls have just been replaced as necessary...that's perfectly fine).

This really isn't a big deal, practically speaking, but entries like these would have me asking follow-up questions as a buyer only because it's unusual see a bottom OH without the top being done as well.  That said, it's very common to see and engine topped at least once between overhauls which has the effect of staggering top and bottom times anyway!
Assuming that you're in the US and operating under pt91 the engine can be run on-condition for as long as it stays healthy.  This could be 4,000hrs over 50yrs if you know how to manage your engine.
If you're dead set on having a "typical" 0 SMOH entry in the logs you'll likely have to have the whole engine overhauled again.  Don't do that.  A bottom with 500hrs is safer than a freshly overhauled engine anyway.
Was it a stationary strike or was the engine running?  What kind of engine is it?

It was an engine running strike.  It is a continental IO-550

"0 SMOH Lower End." means just what it says. The lower end was completely rebuilt but there wasn't a complete overhaul of the "top end". Some of the old top end parts must have been re-used without being overhauled.
I would suggest speaking to the person who did the overhaul to get more information on why the top end did not qualify for 0 SMOH as well.

authors: Шынгыс Жумаш


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What is the purpose of the small wheel at the end of the F-14’s launch bar?

At the end of the launch bar (catapult strop link) on the F-14 airplane, there is a small wheel. Does anyone know what this is used for?

Can you highlight or circle the part in the picture?


text:
Small aircraft performance enhancements due to winglets?
I'm seeing some Beechcraft Barons with winglets.  Do these improve performance and, if so, by how much?

welcome to aviation.se. Did you have a look at our old questions on the subject(https://aviation.stackexchange.com/q/2111/1467 https://aviation.stackexchange.com/q/8556/1467) ? is there something still not clear that you would like explained?


text:
Is a biplane without dihedral more stable than a low wing monoplane without dihedral?
I was wondering if a biplane's top mounted wing created the same stability effect as that of a high wing airplane?
Also, would the unstable effects of the low wing cancel the stability provided by the high wing and condition the biplane to behave like a mid wing airplane? If yes, is it one of the reasons why manufacturers make the top wing longer or is it just extra length provided to generate more lift and replace that lost due to wing interference?
This questions have been bugging me for some time now.
Someone pls clarify me.
Maybe I missed something...

What makes you think that a high wing provides stability?

interesting question

I just thought it did.

Narrow answer: Yes, it is.
But no aircraft designer in his right mind would build an unswept low wing aircraft without dihedral. So this question is misleading.
Please look here why low wing aircraft need more dihedral.
Please read here why a low wing aircraft is just as stable as a high wing aircraft. The high wing does not entail more stability!

Okay. That's new. I always thought a high wing produced a self correcting!

Doesn't a high wing airplane stabilize it self in the roll axis after the pilot centers the stick(without using opposite aileron)? I learnt that the c.g is below the wing and this tends to prevent or dampen roll of the airplane.

Okay. I think I get it. Thanks a lot. That was very helpful.    One more mystery about biplanes; why don't they ever come with a T-tail...now I haven't seen all the biplanes in the world...so maybe it exists. If it does pls share a link or an image. I'm yet to see a biplane with a T-tail or a cruciform tail(as long as the tail is higher than the top wing of the biplane.

@user16656: No. Please read the linked answer, and maybe this one, too.


text:
When must ATC give wind variation and gust?
In connection with takeoff and landing, ATC will give the current wind direction and velocity to the pilot. In some cases, ATC will also report the variation in direction and/or current gust (max and min velocity). This is only done if the variation and/or gust is "significant".
How large does the variation in direction and/or gust have to be before ATC has to report it? Something tells me the mean wind velocity has to be at least 10 knots before wind variation must be reported, but I'm not actually sure.
Please include reference to the relevant regulations or recommended practices (ICAO, EASA or local).

In the USA, we must ensure the pilot has the representative wind (i.e. ATIS) and that's usually it. The only time we must issue the wind on frequency is "when authorizing the use of a runway and a tailwind component exists"—nothing about gusts. That said, if it's gusting above 15 knots or so I'll often toss that in even if it's a direct headwind.

Actually, I think this question needs clarification. Are you asking about the definition of (or the criteria to describe the wind as) "variable" and "gusting"? In that case wbeard's answer would be partially relevant. Or are you asking if ATC has some requirement to specifically issue the wind if it is variable or gusting at such-and-such a level?

@randomhead My local tower issues winds for nearly every takeoff and landing. Is that because it’s materially different from what’s on the ATIS? If so, is that required, or are they doing it on their own?

@Stephen As long as you report having the current ATIS code they are not required to re-issue the wind unless 1) there is a tailwind component (3–5–3) or 2) it is a tower run by the Army, Navy, or Air Force (3–9–10i, 3–10–5e). It is possible that there are or were a large number of ex-military controllers at that tower and they mistakenly trained new arrivals that they always have to issue the wind.

@randomhead The latter. I'm not asking about when variation or gust must be included in the met report, but about when ATC must give these details from the met report to the pilot.


text:
Chinese citizens wanting to get a US pilot license?
I am surprised to see Chinese citizens wanting to get US PPL licenses. The pilot shortage in China does not require anyone to show up with a US pilot license to ask for work. What is driving this phenomenon?

Plenty of people train in the US as there are many flight schools and the costs are very reasonable compared to other locations. Often there's a mechanism to get a license in one's home country on the basis of the US license, or just use the hours and take the practical test in their home country to get a license there.
Additionally, having a US license allows you to fly a US registered airplane, it doesn't matter where in the world it is located, so it could be that many of the airplanes they want to fly have US registrations.

Ok, but having a US license and flying in another country poses other challenges, such as finding a FAA CFI for the mandatory bi-annual review, as well as an FAA AME to renew your FAA medical certificate. I flew my glider for five years in Germany and it was always a challenge (and expensive!) to get the annual inspection done by an IA.

I was wondering... do pilots flying for Chinese airlines get paid extra if they have US licences?


text:
What do the terms 'holding out' and 'common carriage' mean?
A pilot with a new commercial certificate is excited at the new world of getting-paid-to-fly they have opened up.  That is, until their instructor or good friend reminds them of 14 CFR 119 and the grey line that separates operations that do or do not require an operating certificate.
It is cut and dry that a commercial pilot can be paid to do certain things, but when you decide you are going to start doing things for a friend ("yea, I can transport XYZ for you on my next trip to Kalamazoo") things start to get murky. Especially once your friend starts paying you, you make a habit of transporting things and he tells his friends about your service.
At what point are you holding out your services to the public and when do you cross the line from private carriage into common carriage?  How far can you go without an operating certificate.
I'm looking for regulatory answers or anything written from a FSDO, basically anything not anecdotal.

Oddly enough, "common carriage" is not defined in the FAR's, but that is because it is a "common law term" and not specific to aviation.
AC120-12A - Private Carriage Versus Common Carriage of Persons or Property contains guidance that can be used to help determine whether or not an operation falls under common carriage.  Take a look at it for specific examples, but the "plain language" version is:
Common Carriage: A carrier becomes a common carrier when it "holds itself out" to the public, or to a segment of the public.
Holding Out:  A carrier is holding out when they represent themselves as willing to furnish transportation within the limits of its facilities to any person who wants it.
There are lots of ways to "hold out", but the basic idea is if someone in the general public comes to you and asks you to fly them and you agree, you are probably holding out.  Any form of advertising demonstrates a clear sign that you are holding out.  There are also other activities that qualify, so look over the AC if you have further questions, and if that doesn't answer it your best bet is to contact an aviation lawyer.  You could also contact your local FSDO with questions.

As far as transporting a third part for hire, both common and private carriage require an air carrier certificate issued under 125 or 135 depending on the size of the airplane1. This means that your trip for a friend would be in violation because you don't have the required air carrier operating certificate.  (Thank you @p1l0t for clarifying this for me!)
119.23 says:

Operators engaged in passenger-carrying operations, cargo operations,
  or both with airplanes when common carriage is not involved.
(a) Each person who conducts operations when common carriage is not
  involved with airplanes having a passenger-seat configuration of 20
  seats or more, excluding each crewmember seat, or a payload capacity
  of 6,000 pounds or more, shall, unless deviation authority is issued--
(1) Comply with the certification and operations specifications
  requirements of part 125 of this chapter;
(2) Conduct its operations with those airplanes in accordance with the
  requirements of part 125 of this chapter; and
(3) Be issued operations specifications in accordance with those
  requirements.
(b) Each person who conducts noncommon carriage (except as provided in
  Sec. 91.501 (b) of this chapter) or private carriage operations for
  compensation or hire with airplanes having a passenger-seat
  configuration of less than 20 seats, excluding each crewmember seat,
  and a payload capacity of less than 6,000 pounds shall--
(1) Comply with the certification and operations specifications
  requirements in subpart C of this part;
(2) Conduct those operations in accordance with the requirements of
  part 135 of this chapter, except for those requirements applicable
  only to commuter operations; and
(3) Be issued operations specifications in accordance with those
  requirements.

The FAA takes a very dim view of people who start competing with actual air carriers and are unlicensed to do so.  It's a quick way to have your license suspended and end up with some hefty fines and other legal troubles.

1 There are of course the regulations that allow operations "in furtherance of a business" which is why I specified a third party.

I agree with Lnafziger's post with the advisory circular definition of holding out versus common carriage.

"AC120-12A - Private Carriage Versus Common Carriage of Persons or
  Property contains guidance that can be used to help determine whether
  or not an operation falls under common carriage. Take a look at it for
  specific examples, but the "plain language" version is:
Common Carriage: A carrier becomes a common carrier when it "holds
  itself out" to the public, or to a segment of the public.
Holding Out: A carrier is holding out when they represent themselves
  as willing to furnish transportation within the limits of its
  facilities to any person who wants it.
There are lots of ways to "hold out", but the basic idea is if someone
  in the general public comes to you and asks you to fly them and you
  agree, you are probably holding out. Any form of advertising
  demonstrates a clear sign that you are holding out. There are also
  other activities that qualify, so look over the AC if you have further
  questions, and if that doesn't answer it your best bet is to contact
  an aviation lawyer. You could also contact your local FSDO with
  questions."

HOWEVER, and this is the big but that can get you into a world of trouble, just because you have a commercial pilots license and yes you can get legally paid to fly you really cannot carry passengers for compensation. Typically a commercial pilot can have a job like flying skydivers, crop dusting, aerial photography and (with an instructors certificate) provide flight instruction for compensation.
There seems to be a big misconception though that a person can just get a commercial pilots license and take their friends up for compensation. This is false. FAR 1.1 clearly defines commercial operator as:

Commercial operator means a person who, for compensation or hire,
  engages in the carriage by aircraft in air commerce of persons or
  property, other than as an air carrier or foreign air carrier or under
  the authority of Part 375 of this title. Where it is doubtful that an
  operation is for "compensation or hire", the test applied is whether
  the carriage by air is merely incidental to the person's other
  business or is, in itself, a major enterprise for profit.

In fact, inside of AC120-12A itself it even states under Part I:

In summary, persons intending to conduct only private operations in
  support of other business should look cautiously at any proposal for
  revenue-generating flights which most likely would require
  certification as an air carrier.

So while you can fly for hire, you cannot carry passengers or property because then you are acting as a commercial operator. You can work for a commercial operator with that license although for 135 you will need 1200hrs to be PIC. You can do other for hire flying like carrying skydivers, crop dusting, banner towing or aerial photography though as perscribed in the only exceptions stated in FAR 119.1(e).
If you want to fly with your friends you cannot charge them for your time. You could be flying to a business meeting and happen to be on the clock anyway but you cannot specifically charge for the transportation. What you also can do (even as a private pilot) is share costs. FAR 61.113 says:

A private pilot may not pay less than the pro rata share of the
  operating expenses of a flight with passengers, provided the expenses
  involve only fuel, oil, airport expenditures, or rental fees.

To summarize a commercial pilots license allows you to fly for hire but does not allow you to act as a commercial operator and carry persons or property other than as an air carrier. You can work for someone who has that certificate but you can't just rent or buy a plane and charge a passenger for your time as pilot legally even as a commercial pilot. You can only split costs with them just like you could as a private pilot.
Traps For The Unwary: Business Flying And The "Compensation Or Hire" Rule
Now I have seen some mentions of trying to get away with Part 91 Subpart K as well. § 91.1005 Prohibitions and limitations.
(a) Except as provided in § 91.321 or § 91.501, no owner may carry persons or property for compensation or hire on a program flight. FAR 91.501, however, is going to say this:

(b) Operations that may be conducted under the rules in this subpart
  instead of those in parts 121, 129, 135, and 137 of this chapter when
  common carriage is not involved, include—
  (1) Ferry or training
  flights;
  (2) Aerial work operations such as aerial photography or
  survey, or pipeline patrol, but not including fire fighting
  operations;
  (3) Flights for the demonstration of an airplane to
  prospective customers when no charge is made except for those
  specified in paragraph (d) of this section;
  (4) Flights conducted by
  the operator of an airplane for his personal transportation, or the
  transportation of his guests when no charge, assessment, or fee is
  made for the transportation;
  (5) Carriage of officials, employees,
  guests, and property of a company on an airplane operated by that
  company, or the parent or a subsidiary of the company or a subsidiary
  of the parent, when the carriage is within the scope of, and
  incidental to, the business of the company (other than transportation
  by air) and no charge, assessment or fee is made for the carriage in
  excess of the cost of owning, operating, and maintaining the airplane,
  except that no charge of any kind may be made for the carriage of a
  guest of a company, when the carriage is not within the scope of, and
  incidental to, the business of that company;
  (6) The carriage of
  company officials, employees, and guests of the company on an airplane
  operated under a time sharing, interchange, or joint ownership
  agreement as defined in paragraph (c) of this section;
  (7) The carriage of property (other than mail) on an airplane operated by a
  person in the furtherance of a business or employment (other than
  transportation by air) when the carriage is within the scope of, and
  incidental to, that business or employment and no charge, assessment,
or fee is made for the carriage other than those specified in
  paragraph (d) of this section;
  (8) The carriage on an airplane of an athletic team, sports group, choral
  group, or similar group having a common purpose or objective when there is
  no  charge, assessment, or fee of any kind made by any person for that
  carriage;
  and (9) The carriage of persons on an airplane operated by a person in the
  furtherance of a business other than transportation by air for the
  purpose of selling them land, goods, or property, including franchises
  or distributorships, when the carriage is within the scope of, and
  incidental to, that business and no charge, assessment, or fee is made
  for that carriage. (10) Any operation identified in paragraphs (b)(1)
  through (b)(9) of this section when conducted— (i) By a fractional
  ownership program manager, or (ii) By a fractional owner in a
  fractional ownership program aircraft operated under subpart K of this
  part, except that a flight under a joint ownership arrangement under
  paragraph (b)(6) of this section may not be conducted. For a flight
  under an interchange agreement under paragraph (b)(6) of this section,
  the exchange of equal time for the operation must be properly
  accounted for as part of the total hours associated with the
  fractional owner's share of ownership.

So if you think that you can fly as a "private carrier" under Part 91 and charge for it and not be found as needing a 135 air carrier certificate (or maybe 121, 125, etc..) you are in for a world of hurt. AOPA Legal Counsel Offers a nice write up on some of the differences between having a CPL and being a commercial operator. The exceptions to this rule are the ones in 119.1(e) as mention before (aerial photography, etc..).
Why "private carriage" does NOT relieve you of getting an air carrier certificate. Even if you are found to be private carriage FAR 119.23(b) clearly states:

(b) Each person who conducts noncommon carriage (except as provided in §91.501(b) of this chapter) or private carriage operations for
  compensation or hire with airplanes having a passenger-seat
  configuration of less than 20 seats, excluding each crewmember seat,
  and a payload capacity of less than 6,000 pounds shall—
(1) Comply with the certification and operations specifications
  requirements in subpart C of this part;
(2) Conduct those operations in accordance with the requirements of
  part 135 of this chapter, except for those requirements applicable
  only to commuter operations; and
(3) Be issued operations specifications in accordance with those
  requirements.

Guess what Subpart C of 119 is going to say:

§119.33   General requirements. (a) A person may not operate as a direct air carrier unless that person—
(1) Is a citizen of the United States;
(2) Obtains an Air Carrier Certificate; and etc..

So any notion that you can fly for compensation other than exceptions in 119.1(e) is FALSE unless you also possess the appropriate operating certificate.

"You can work for someone who has that certificate but you can't just rent or buy a plane and charge a passenger for your time as pilot legally even as a commercial pilot. You can only split costs with them just like you could as a private pilot." I'll have to disagree with this comment. As long as you didn't hold out to your friend and your friend approached you first, you can provide him or her with your service as a commercial pilot for compensation. If you don't hold out, you're providing private carriage.

@lemonincider The problem is you said YOU are going to buy the plane. (Even if you rent from someone else than THEY would have to have an air carrier certificate). You cannot charge money for a flight and not fall under Part 119. Remember there are only a few exceptions defined under Part 119 that allow you to operate Part 91 instead 135 or 121 or whatever. Now if you are flying for someone else who owns their own plane and the flight itself is NOT for hire (family / friends) than you could charge for your time as a pilot and there would be no need for the air carrier certificate.

Advisory Circular 120-12A
According to part D, it would seem that when you have long-term contracts to serve somewhere between 3 and 18 customers are you likely to be considered a common carrier.
But what they're getting at is that those guys who had 18-24 had the ability to serve 18-24 clients at max. So while they were still working private contracts and not open to the general public, they were accepting as many contracts as they were able, which is really no different than holding out to the public. But if you have three full-time aircraft and are flying contracts for two clients on a semi-regular basis, you are not likely to be seen as holding out.
This is a very hard thing to define because there is no right answer. The definition varies between FSDOs and even between operations in question. If you do a lot of research you'll find that the FAA tends to be conservative and will say that operations that may blatantly fall under private carriage via 120-12A's guidelines must still be a 135 operation or worse. Then another case that strikingly similar might come up and the ruling is that it's okay.
The only real way to know where that line turns from light gray to dark gray is to call the FSDO and ask.

Yes but he seems to think that private carriage means that he doesn't need an air carrier certificate or an operating certificate for that matter and this is false. According to FAR 119.23(b) even private carriage is subjected to Subpart C and an air carrier certificate.

@p1l0t: but if you are not operating as common carriage, Part 119 is only applicable to aircraft with at least 20 seats or 6000 pounds payload.

@Qantas 94 Heavy FALSE. (b) Each person who conducts noncommon carriage (except as provided in §91.501(b) of this chapter) or private carriage operations for compensation or hire with airplanes having a passenger-seat configuration of less than 20 seats, excluding each crewmember seat, and a payload capacity of less than 6,000 pounds shall—

@p1l0t: then is §119.1(a)(2) not misleading?

Part a refers to aircraft with more than 20 seats, part b refers to aircraft with less than 20 seats. Either way you need a 135 certificate unless you fall under the specific exceptions in 119.1(e)

I believe answers so far to this question are incorrect.
14 CFR 119.23(a & b) was referenced to disallow a commercial pilot from engaging in all private carriage. However, Part 119 would not apply to several instances. Look at 14 CFR 119.1(a) -

Blockquote This part [that is all of Part 119] applies to each person operating or intending to operate civil aircraft—

Blockquote (1) As an air carrier or commercial operator, or both, in air commerce; or

Blockquote (2) When common carriage is not involved, in operations of U.S.-registered civil airplanes with a seat configuration of 20 or more passengers, or a maximum payload capacity of 6,000 pounds or more.

119.23(b) is written with this applicability in mind so you must interpret it with its applicability context in mind. So 119.23(b) does not rule out someone conducting private carriage in an aircraft with less than 20 passenger seats or a max payload less than 6,000lb.
14 CFR 91.501(b) was referenced to disallow a commercial pilot from engaging in private carriage. However, 91.501(a) indicates Part 91 Subpart F (under which 91.501 is found) is only applicable to certain airplanes or operations under 91 Subpart K (fractional ownership) only. If the type of operation is not a fractional ownership operation, then this objection is moot.
The way I understand it, if a company X buys a small airplane, and hires a certificated commercial pilot to fly their executives around, the commercial pilot can be compensated for his flying the airplane.

Not sure that this provides an answer to the stated question. Stack Exchange is a Question & Answer forum, not a discussion forum, and while discussing aspects of a posted answer in chat is okay, replying to an answer with an "answer" post that doesn't actually provide an answer to the question, is not.


text:
How many pilots do long flights need?
Under normal 2 pilot part 121 ops I could only be scheduled to fly 8 hours in a given day.  This is plenty for the routes we flew (longest leg around 4 hours) so I never encountered the rules for longer flights.
For flying beyond 8 hours -- long haul international ops -- what determines how many pilots must be on board?  Is only flight time taken into account or is the number of timezones crossed also a factor?

The regulations for this are in 14 CFR 121 Subpart R—FLIGHT TIME LIMITATIONS: FLAG OPERATIONS.
In short, flight time limits within a rolling 24 hour period depend on the number of crew members assigned to the flight:

One or two pilot crews - 8 hours max
Two pilots and one additional flight crewmember: 12 hours max
Three or more pilots and an additional flight crewmember: More than 12 hours, but "adequate sleeping quarters on the airplane" will be provided

However, they may also implement a "Fatigue Risk Management System" which allows them to exceed these limits if they are found to be safe and approved by the FAA.  This system would most likely address the number of timezones crossed but is optional.
A particular airlines pilot contract may also have more restrictive limitations (like considering the number of timezones crossed) that are negotiated by the union, but this is not required by the regulations.

§121.481   Flight time limitations: One or two pilot crews.
(a) A certificate holder conducting flag operations may schedule a
  pilot to fly in an airplane that has a crew of one or two pilots for
  eight hours or less during any 24 consecutive hours without a rest
  period during these eight hours.
...
§121.483   Flight time limitations: Two pilots and one additional flight crewmember.
(a) No certificate holder conducting flag operations may schedule a
  pilot to fly, in an airplane that has a crew of two pilots and at
  least one additional flight crewmember, for a total of more than 12
  hours during any 24 consecutive hours.
...
§121.485   Flight time limitations: Three or more pilots and an additional flight crewmember.
(a) Each certificate holder conducting flag operations shall schedule
  its flight hours to provide adequate rest periods on the ground for
  each pilot who is away from his base and who is a pilot on an airplane
  that has a crew of three or more pilots and an additional flight
  crewmember. It shall also provide adequate sleeping quarters on the
  airplane whenever a pilot is scheduled to fly more than 12 hours
  during any 24 consecutive hours.
...
§121.495   Fatigue risk management system.
(a) No certificate holder may exceed any provision of this subpart
  unless approved by the FAA under a Fatigue Risk Management System.
(b) The Fatigue Risk Management System must include:
(1) A fatigue risk management policy.
(2) An education and awareness training program.
(3) A fatigue reporting system.
(4) A system for monitoring flightcrew fatigue.
(5) An incident reporting process.
(6) A performance evaluation.

Does this change at all with the new regulations in 14 CFR 117?

@casey Yes, that's the first I've heard of that (can you tell that I'm a 135 guy and not a 121 guy??  :))!  This would still apply to 121 cargo flights as 117 is for passenger flights only.

Does this apply to business aviation as well?


text:
What are the rules of airfoil thickness from root to tip on tapered wings?
I'm doing some research on wings and airfoils used in the 30s and 40s, and I'm trying to understand the rules about airfoil proportional thickness changes across the wing (root to tip) on tapered wings.
Many planes of that time used airfoils with thickness ranging from 15% to 9% (root to tip). (Source: https://m-selig.ae.illinois.edu/ads/aircraft.html)
So the question is: what are the rules for dimensioning airfoil thickness from root to tip?

There are no clear rules; choosing wing thickness was no rigid science.
However, some rules did exist:

Root thickness goes up with aspect ratio. While "regular" wings (aspect ratio between 5 and 8) had a root thickness between 14% and 18%, the high aspect ratio Davis wing (AR 11) needed a 21% root airfoil.
Tip thickness was chosen for maximum section lift in order to add stall margin and aileron authority. This means thickness here is between 9% and 12%.
Camber also reduces from root to tip proportional to the lift per area ratio. While the inner wing should produce the highest lift per area, the outer wing reduces this for stall margin and better aileron authority with upwards deflected ailerons.
In the early jet age, high speed required thinner wings because this delays the onset of Mach effects. The symmetrical tip airfoil of the Me-262 had 9% thickness and supersonic aircraft reduced wing thickness to 6% to 4%, the thickness of the Bell X-1E wing.

Airfoil thickness at the root was chosen to obtain a good cantilever ratio: the bending moment is highest there, and you need to give it structural height. Also, you want to create most lift at the wing root, that is why chord, thickness and incidence angle are all highest there. All three tapering down towards the tip for structural reasons.
There is a bit more info in this answer.

The term for the draftsman's job of airfoil depiction in the, 30's and 40's, was called "Lofting". Maybe the term is still in use, today.
Airfoils camber would be defined as a percentage of the chordline dimension, either above or below the chordline. In the day, a table of points along the chordline would have corresponding (+%) or (-%) values to be plotted and then connected via a draftsman's French curve template.
When making the drawings for the tapered wing's ribs, the camber diminishes proportionally with the length of the chord.

Thanks for you reply. Where can I found references about this?

Off hand, I sure don't know. I would have to just do www searches, myself. Sorry I can't be of more help.

I would like to know why not use the same airfoil from root to tip, keeping same proportional thickness and camber.

As an anecdote, the term lofting comes from shipbulding, when the curves between hull frames were fitted on a 1:1 drawing... in the loft above the shipyard, which is the only place those drawings would fit. The term is still in use, although it is falling out of the common parlance.


text:
Isn't it dangerous to sell alcohol inside of airports?
Why do they sell alcoholic beverages inside of airports?
Since it is flammable, it could be possible that someone buys some bottles (I believe up to 5L per person), and could decide to start a fire on board. Isn't this very dangerous?
PS: you can also buy lighters in the airport! How is it possible?

@vasin1987 you are probably thinking about the duty free allowance.You are free to buy more, but you have to pay taxes for it.

and why don't we forbid LiPo batteries? (obligatory link: https://xkcd.com/651/ ) because sometimes regulations are not meant to be, let's say, "smart"

I heard that they also allow you to wear clothing (flammable!) and even hair (highly flammable!), which I find way more dangerous!

To put @JörgWMittag's comment more politely, because there's compromise in everything. People are willing to take the risks you outline so they can enjoy a drink themselves.

Thanks for the sarcas @JörgWMittag ... let's put it this way... why don't they sell me some gasoline... after all it is not so dangerous as bringing 5L absinthium 70% on board no? :)

@FedericoGentile because there's no good reason for you to have gasoline, there are many good reasons for alcohol.

This is really difficult to answer because there are so many possibilities and so many of them are theoretical. For example, why burn the alcohol - with very little control over the results - when you can just smash the bottle and use the sharp glass as a weapon to threaten the crew? Why not buy a pencil and use it like a dagger? Why not buy a belt and use it as a garrote? Etc. Open-ended security questions are rarely useful because almost anything can be presented as a 'threat'.

I'm voting to close this question as off-topic because it belongs on Travel.se instead.

yes true nothing to do with aviation safety/security.... please give a break... I see that someone was able to give a proper answer to my question!

@RalphJ Being on-topic somewhere else isn't a reason to close. Your custom close reason should explain why the question is off-topic here.

Most alcoholic drinks are, in fact, nonflammable because they're mostly water.
The original definition of "proof" was that 100-proof was the minimum alcohol content required for a pellet of gunpowder soaked in the drink to still be able to burn. That corresponds to about 57% ABV, which is considerably stronger than most spirits. (The current definition of proof used in the US is that 100-proof means 50% ABV; the rest of the world, as far as I'm aware, has discarded proof and just uses ABV.) So, unless your alcohol is extremely strong, you can't even burn gunpowder in it. Beer would be about as good as water for putting out fires; probably wine, too.
You're probably thinking that alcoholic drinks are flammable because of their use in cooking. However, the reason you see impressive sheets of flame when a chef pours alcohol into a pan is that the pan is very hot. The heat instantly boils the alcohol and the chef then sets fire to the vapour above the pan. If, instead, they allowed the dish to cool to room temperature, then added the alcohol and dropped a match in the pan, the match would go out.
The real danger of selling alcohol in airports is people getting drunk. People do get obnoxiously drunk in airports and on flights and it relatively often causes problems – every few weeks you hear about a flight being diverted to deal with a violently drunk passenger. But, at the moment, it's felt that it's not a big enough problem to come close to banning the sale of alcohol.
You can buy lighters in airports because you're already allowed to carry them with you through security. Most things on a plane are reasonably well fire-proofed so somebody setting fire to their clothes or something like that can probably be dealt with by dumping a fire-extinguisher on then, before the fire spreads. And anybody lighting a lighter on a plane will attract immediate attention from everybody around them, followed by the cabin crew, followed by the police after landing.

Why do they sell alcoholic beverages inside of airports

Because they can!! Simple as that. Most countries has no regulation against selling alcohol to adults as long as they are not clearly intoxicated. If you appear intoxicated at any point of journey you may not be allowed to continue your flight though.
United Airline's website states the amount of alcoholic beverage that can be carried on board. With a note that the bottle cannot be open in flight.
So basicly if a passenger opens a bottle and try to set aircraft on fire, the passenger is treated as unruly and dealt with accordingly.

You can even buy Swiss pocket knifes in Geneva. Of course they are sealed in a plastic bag.
Nowadays airport security is beyond reason, and what you can take through and what not has only little to do with security.

indeed, ever more I've the feeling it has more to do with providing business for the shops in the departure lounge. Confiscate your bottled water so you're forced to pay 5 Euro+ for one after you clear security, with the airport no doubt getting a cut...

@jwenting It's not the airport that decided you can't take liquids through security. And the cut of the shops profits that the airport takes is called "rent", just like everywhere else.


text:
Is there a 3-dimensional airspace viewer?
I am using SkyVector to have an idea of what the airspace looks like in terms of waypoints and airways.
I was wandering if anybody knows a website that displays such information but in 3D (or 3D + time) in order to navigate through the airways and check out some information as viable flight levels or altitude constraints.
I am imaging of a website/software that allows to navigate like on google earth or cesium and see what the airspace is like (qualitatively at least).

These guys have some ambitious and very interesting plans. They're taking pre-orders for shipping in 2017Q3, but from what I've read they did that a year or more ago and then announced a big delay.

There are some usable Google Earth plugins, though they can be slow and imperfect.

You can download Google Earth airspace files for most countries, and move through them in 3D to explore what they would look like for various areas.  For example, you could see where you would be "under" a Class B shelf, or where you might navigate to avoid B/C/D airspace and "surface airport E airspace" (if you're flying an ultralight, for example).
These files can be downloaded from 3dairspace.org.uk
Here is a screenshot I just captured of the Seattle Class B, looking northwest from the southeast corner.


text:
Where to find comprehensive description of Special Use Airspaces (SUAs)?
Can you suggest me some document or website where I can learn about Special Use Airspaces?
My goal is to understand the following topics:

SUA definition
Types of SUAs
SUA pubblication
SUA creation and activation
Documents in which SUA geometry and time information are stored.

If you know some website, pdf or book where I can learn about SUA I would be very glad. Feel free to add to the answer also your suggestions and knowledge about what you know relative to SUAs (especially about where geometry and time infos are stored).
Note: I know wikipedia or eurocontrol have some definitions but they are too concise for me. I would like to get something quite detailed and complete.

SUA definition what's not clear from your previous question?

As you can read on the question I would like to have a document/website with a comprehensive description of SUAs... the answer you gave me are clear but come from people. I would like to have somehow the bibliography where they got the infos from.

This page has SUA geometry and time information for active SUAs. https://sua.faa.gov/sua/siteFrame.app

Which country/countries are you interested in?

As many as possible... especially EU and USA but also South America, Asia, Oceania :)

The definition of Special Use Airspace according to Wikipedia are:

Is an area designated for operations of a nature such that limitations may be imposed on aircraft not participating in those operations. Often these operations are of a military nature.

Types of SUA's

restricted airspace, prohibited airspace, military operations areas (MOA) and temporary flight restriction.

Two relevant PDF documents:
https://www.faa.gov/documentLibrary/media/Order/7400.8SBasic.pdf
https://www.faasafety.gov/files/events/GL/GL05/2007/GL0515004/CH_3_Sec_4.pdf
Wikipedia link: https://en.wikipedia.org/wiki/Special_use_airspace

Hi, yes I need much more information of that because that is what I already know (as stated in my question).


text:
Are there any methods to predict the location of a jet aircraft from its sound?
At times there are military fighter aircraft flying overhead of my location (MiG-21Bis and Su-30MKI).
The first indication of their presence being the sound, that obviously causes one to look up to try and acquire them visually. The sound can be distinctly made out to be changing, as if for a moving object (not sure pure Doppler shift and/or change of source location).
However, almost all the times the aircraft are actually sighted in a totally different location from where the sound 'seems' to indicate them to be (and sometimes not sighted at all)! This seems obvious due to the relatively slow speed of sound and the fast speed of the aircraft.
However, are there are any suggested method(s) to locate such aircraft visually based on the sound?

It's really not different from any wave-based passive detection like radar, sonar, etc. With a large enough receive aperture and high enough signal to noise ratio you can do it definitely, and has been done.

The Problem with localizing air crafts by their sound is: sound is slow.
The speed of sound is roughly 300m per second.
eg.: If an aircraft is 2km away its sound needs about 6 seconds to reach you. During this time an aircraft traveling at 600km/h moves 1km.
It is quite likely that you hear the sound from high flying airfrafts after it passed your position. This likeliness increases with the speed of the aircraft and reaches 100% for supersonic flights.
Furthermore the air craft can do any maneuver within the time its sound travels to you.
This means that you, at best,  can estimate an aircrafts  position  by sound analysis. The accuracy you can get is far to worse to either use it for air traffic controlling or anti air missile guidance.

I myself wrote in the question due to the relatively slow speed of sound and the fast speed of the aircraft, so I understand this issue...

However, in the first world war, at least the aircraft themselves were slow. http://rarehistoricalphotos.com/aircraft-detection-radar-1917-1940/


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Why are only some aircraft in this formation creating contrails?
The Republic Day celebrations at New Delhi, India had a series of flypasts by the Indian Air Force.
What struck me the most was that in a formation with a C-17 in middle and two Su-30MKI flanking it, there were contrails visible from the Su-30MKI but not from the C-17:

Both the C-17 and Su-30MKI have turbofan engines. For C-17, Pratt & Whitney F117-PW-100 and for Su-30MKI Lyulka AL-31.
As per 'How does contrail formation differ from turbofan to turbojet?', contrails depend on the bypass ratio of the turbofan engine:

(...) higher bypass engines available today increase the contrail occurrence.

As per available sources, the F117 has a bypass ratio of 5.9:1 and the AL-31 has a bypass ratio of 0.59:1. So, the F117 has higher bypass compared to the AL-31 (or maybe I'm wrong).
What would be the reason that in the first two photographs, the C-17 engines do not form contrail whereas the Su-30MKI seem to?
One possibility is that, this difference is due to possible different power settings on the two aircraft engines for the same speed (considering the different intended role).
Another thing was that such contrails were not visible on any other fighter aircraft (e.g., Tejas/LCA). Or even another pair of Su-30MKI along with a AEW&CS aircraft:

Notes:

Sorry for the poor quality of photos due to the poor visibility in Delhi (winter fog/smog).
Some photos are here:

thequint.com
blogs.wsj.com
indiatimes.com

Are you sure that they weren't using some sort of smoke generation system? Those don't look like contrails to me.

@RonBeyer not sure/aware about smoke generation... But now that you mentioned it, I also doubt these are contrails...

Absolutely not contrails. Smoke generators for sure. Actual contrails, condensation from the motors, won't form near sa level in warm air.

And amazingly, in that second pic the Sukhoi's can apparently produce a giant bird in their trails! :D

They must be chemtrails

Should be added that the reason that aircraft in airshows often leave smoke trails is to aid civilian visibility. People who are not accustomed to "looking up" often have difficultly locating the airplane(s) in the sky.

Conspiracy theorist would probably claim the jets are fumigating the population, and the C-17 not.

From: Forum post - "Trails from the back of Fighter Jets", Metabunk.org

Jets practicing for air-shows (or actually in air-shows) sometimes use smoke to create trails. This is made by injecting something like paraffin into the hot exhaust where it vaporizes and condenses as smoke.

And the accompanying image

Looks a lot like the image in your question.


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How is the terrain displayed on the ND in a A320?
When you turn on "TERR ON ND" in a A320, you see terrain info on you navigation display (ND), but where does its source come from ?

if data comes from FMGS stored inside its memory, then how come it cannot display it in all bounds of the display (see picture) ?

if data comes from the nose radar, then how is it possible to see oceans when you're on the ground in an airport, say in JFK for example ? The radar beam would never be able to get to the water directly.

how come it cannot display it in all bounds of the display (see picture) ? uh? I've seen the picture, but I don't get what you mean with "all bounds of the display"

I mean like below the aircraft for example (and on the sides)

aircraft are non-holonomic systems, they can't move sideways and they can't pull back mid-air, so way waste precious screen real-estate for stuff that does not influence you?

On the sides, for better situational awareness, if you need to pull a steep turn

an A320 is not a fighter, its manoeuvrability is limited. you can be sure that they evaluated this when deciding exactly which angle to display

Matt, can you provide a link to the page containing the image (first for mandatory credit, and then for understanding the context)? This content is the EGPWS, based on an elevation map stored into the avionics, so water areas are identified. Colors depict relative altitudes. See page 429 of this FCOM.

Regarding the area displayed: The full 180° are only covered by the recent versions of the EGPWS. the reason is likely that calculating relative altitudes is a heavy workload for the EGPWS CPU, and with new chips, more pixels can be computed in a decent time. See how slowly the display is refreshed in this video.

http://aircockpit.com/viewtopic.php?p=49417&sid=f4823eeafd9cfef861a0928e5cec1729

Ok, so I guess it is a misinterpretation when people talk about "radar", when it's actually already in the FMGS.

Not in the FMGS, the EGPWS is an alerting device, it doesn't actuate any control of the aircraft, it provides altimetry data and alarms that happen to be displayed on the same display than some navigational information from the flight computer. See Gerry's answer.

The terrain data is contained in a database within the EGPWS (Honeywell TM) or the Terrain Awareness and Warning System (TAWS) as defined in the regulations -- can't use a trademark in the regs.
The discussion in your link about "blockiness" when zooming in is a result of the database grid references.  To save memory space, the resolution of the world-wide terrain data varies based on terrain variation and it's relative hazard to flight operation.  There's greater resolution (smaller grid) near airports and in mountainous areas.
The A320 does have airborne radar that is capable of displaying "weather" which really means precipitation.  It can't be displayed at the same time as the terrain to avoid confusion.
Neither the EGPWS or the radar data are in the FMGS.  Their data is just underlayed on the navigation display.  (EGPWS does receive data from the FMGS to support it's warning functions.)
TAWS/EGPWS function is described in TSO-C151c

It just seemed confusing when you look at how the terrain display updates itself: it doesn't update visually by top to bottom, but instead, by radials of a circle (just like weather radar)...

That's a consequence of designing the system to the least common denominator.  When Allied Signal (now Honeywell) designed the EGPWS in the mid 90's, a major criteria was that it had to be retrofitable into the majority of the fleet.  A big issue was the availability of a display for the data.  Since almost all had a dedicated weather radar display the decision was to 'share' the display.  That meant using the same physical interface to the display (via an external switch) and data format.  As a result, the terrain data is drawn in the same manner as the radar displays the weather.


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What is recurrent training?
Is it taken by both pilots and flight attendants? How frequently? What is the main purpose of it? Is it mandatory?

Recurrent training is required annually by the FAA for both pilots and cabin crews, by 14 CFR 121.427.  I am only familiar with the content of recurrent training for flight attendants so this answer is limited to them only.  In a previous answer I wrote:

Annually we would be required to attend jet recurrent training where we reviewed NTSB accident reports with an emphasis on cabin crew responses to emergencies, review of first aid and CPR techniques, re-testing of our knowledge of the location and how to use all the safety equipment on board, including life preservers, life rafts, and emergency slide procedures. We were also briefed on any changes to FAA mandated procedures and tested on everything.

The purpose of the training is to refresh our knowledge of required safety procedures that might have gotten rusty and to stay up to date on possible changes to FAA required procedures.  Emergency procedures are almost never needed and yet it's vital to be able to recall them when needed.  One day a year was devoted to recurrent training and you had to pass all the tests to stay current.  For this reason, we took it very seriously.

Recurrent training must be conducted regularly, under most rules (EASA, FAA etc) 2 simulator sessions twice a year. It is mandatory, basically to prove to authorities that the pilots are still up to handling emergencies according to the airline handbooks.
Because airliners are so safe nowadays, nothing happens. My apologies for oversimplifying this, but pilots fly from A to B and back to A again year after year, and nothing happens. So then they find themselves in a Level D flight simulator, and everything happens: engine fail, dual hydraulic fail, smoke in the cockpit, alarms going off, "woop woop Pull Up!"
It is a very useful requirement for keeping everybody sharp and on top of things. The exercise is not an automatic pass - upon a fail a pilot can get a re-assessment. Fail this again and continued employment can get hairy.


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Why are there missiles under the wings of this Dassault Falcon?
While browsing Flightradar this afternoon, I managed to land on this aircraft, but then I noticed that that's a Falcon 20D with a sort of missile pod under the wings; is that a training aircraft for military purposes or is this a sort of meteorological device?

(jetphotos.com)

(Flightradar24)

You say "Falcon". I think "F-16", followed by why wouldn't it have missiles under wing?? Then I realize "not that Falcon"...

@FreeMan - F-16 and other fighters also carry similar 'things that look like a missile but are not actually a missile'. Same shape/size/weight of a real AIM-9, but no warhead and no missile motor. Full sensor and circuitry, and can get a tone and lock on a target, exactly like a real missile. This is the normal daily training load.

I've heard of a Fighting Falcon before, but this is ridiculous!

These pods aren't missiles or weather radars, but used for electronic warfare. They are mounted on aircraft attachments and connected to control panels in the cockpit. They are not dropped. It's difficult to determine what they are exactly made for, externally they look more or less the same.

Falcon 20 (G-FRAW) pods, in 2012, source

Falcon 20 (G-FRAR) pods, in 2010, source
[
Falcon 20 pods, source
Cobham was acquired by Draken in 2020. It's a contractor in operational readiness training for UK MoD and US DoD. The pods may be in-house developed or provided by their customers. From this article:

Although the Cobham jets are civilian, they work closely with the MOD and play a major role in proceedings. They are equipped with onboard systems and special electronic warfare mission pods for radar and communications jamming, threat simulation and electronic surveillance.

As Bianfable mentioned in a now deleted answer, they can also record electronic signals during the exercise for post-exercise debriefing.
The image you included is from the 2021 Joint Warrior exercise in UK. A typical use can be found in this article, the exercise involves both Royal Air Force and Royal Navy:

An example exercise could be to provide general communications jamming before approaching the ship with two Hawk aircraft flying in close formation with a Falcon 20. The Hawks then accelerate away towards the target to simulate air launched, sea-skimming anti-ship missiles. At the same time, the Falcon uses its under wing threat emitter to simulate a specific missile’s seeker.

The aircraft is part of a fleet of 20 Dassault Falcon 20. It frequently participates to this exercise, and is also visible in this video for the 2017 edition, starting at 12:12 carrying different pods, of which one looks similar:

Falcon 20 at Glasgow Prestwick for Join Warrior 2017, source
The gray material used at both ends, and for the fins is a radome material, transparent to waves, covering receiving and transmitting antennas.
Example of pod housing the AN/ALQ-167 radar jammer:

AN/ALQ-167 radar jammer, source

I wouldn't have expected fins on something that wasn't intended to be separated from the aircraft; do you know why they're present?

@RussellBorogove I could be wrong, but I don't think they're fins - they're stabilizers. No matter how securely the pods are mounted to the wing, there will always be tension and, therefore, vibration as the air shifts across the device during flight. The stabilizers would act to moderate and minimize that air-driven vibration, which could be damaging to the purpose of the pods.

@RussellBorogove: You're right, these fins have no directional role, but are aerodynamic radomes for additional antennas (e.g. a VHF array). Example in this patent, (item 216). Some pods have them, other not, and sometimes radomes have a specific shape. I added pictures with variants. Similar to antenna/drain fins.


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What dialogue would a crop duster typically have with ATC?
By Stefan Krause, Germany (Own work) [FAL], via Wikimedia Commons
What is the exact dialogue a crop duster pilot will have, if any, with ATC on a routine flight?

Are you wanting to know everything from startup to shutdown, or just part of the flight? Also, what country or area are you interested in?

What? Crop dusters with radios? What is this world coming to? Hmm, maybe I'm a little out of date. The last time I was in a crop duster was in 1956.

The current answer and its comment show that this is actually possible to answer this question easily. VTR.

Typically, no communication will take place with ATC, because most crop dusting will take place in uncontrolled airspace, or at least outside of airspace requiring communication with ATC. However, it is not uncommon for a crop duster to do some traffic advisory communication over CTAF if operating out of a public use airport. In my flights in the vicinity of crop dusters and crop dusting operations, I have heard CTAF traffic calls on a few occasions, at what I would estimate to be 10% of operations at public use airports.

The actual operation of a crop duster airplane will almost invariably happen in uncontrolled airspace. In the US, controlled airspace does not start until 700, 1200, or in a very few select areas 14,500 feet above ground level; below that the airspace is Class G, uncontrolled. Crop dusters operate at a few hundred feet above ground level or lower (a quick google shows altitude as low as a few tens of feet AGL). Even if they wanted to talk to ATC at those altitudes, radio reception would be all but impossible.
When not actually working on a field crop dusters must adhere to the standard minimum altitude rules (500 feet AGL over non-congested areas, or 1000 feet above the tallest obstruction within 2000 feet over congested areas). But even if they enter Class E airspace, which is controlled, they do not have to contact ATC unless they want to receive an instrument flight rules clearance.
There are three times when a crop duster would have a dialog with ATC: when they want to come into a controlled airport to land, when they want to transition the airspace close to a controlled airport (where the controlled airspace extends to the surface), or when they want to operate over a field within the controlled airspace near an airport. For the first two situations they would communicate with the tower just like any other aircraft; for the last situation it might sound like this:

Duster: Podunk Tower, hello, Air Tractor 123AT is eight miles to the east, we'd like to operate over a field inside the Class Delta airspace two miles east of Podunk Airport.
Tower: Air Tractor 123AT, Podunk Tower, the Podunk altimeter 2992, proceed as requested and remain east of runway 18/36.
Duster: Proceed as requested, remain east of 18/36, Air Tractor 3AT.


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Twin otter engine starting procedure
Could you please give me the steps or procedure to start the a/c twin otter gas turbine engine?

Are you the owner? It should be in POH then. Otherwise can you provide more context why you want to know this procedure?

I am not an owner, but just want some info only.

For generic info http://aviation.stackexchange.com/questions/1959/how-are-turbine-engines-started

At the beginning of this video you can see the start up (done pretty quickly). Just turns on electric (above left window), checks battery, turns on fuel pumps (bottom middle panel) and then switches on the (electric) starter (above left window), waits a little for the engine to start turning and opens the condition lever (overhead panel) and waits a bit more for the engine to reach idle rpm.


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What is the difference between reversible and irreversible controls?
What is the difference between reversible and irreversible controls ?

Reversible means: at the flight controls, the aeroforces at the surface can be felt. The hinge moments exerted onto the control surfaces (ailerons, elevator, rudder) by the airflow are fed back (reversed) to the pilot - holding the control surface at a certain angle requires a pilot force at the stick, creating a moment at the stick that equates the aerodynamic hinge moment at the control surface hinge.
Irreversible means: the pilot cannot feel the forces and moments that the airflow exerts on the control surfaces. They will definitely need some sort of artificial feel that links force to control position: humans have very precise force transducers in his hands, but no position transducers. So in order to get an intuitive measure of how much the flying control is deflected, an artificial resistance force is exerted by a spring based feel system. Deflecting a valve that results in oil flow that deflects a rudder, requires no force at all by itself. A limp light stick at M 0.85: not a good idea, that's why the artificial feel system is required.
Irreversible flight controls are usually hydraulically powered, but not every hydraulically powered flight control is irreversible. Aeroforces have a couple of desirable feel characteristics that are not easy to mechanically reproduce, mainly the stiffening up of the spring force as the aircraft picks up speed. In some aircraft the hydraulic actuators act as boosters: they amplify (boost) the control forces of the pilot. In the F100 the elevator is powered for 1/3 by the pilot and for 2/3 by the hydraulic actuator, and the pilots feel the airforces directly but only part of them. No artificial feel system required.
Some aircraft have irreversible flying controls with artificial q-feel, which stiffens up the spring gradient when IAS picks up, just like with reversible controls. The B737 pitch control column for instance.

It is easy to understand it if you think this way:

The control force goes 'forward' from the yoke/stick/pedals to the control surface (e.g. rudder).
The (mostly) aerodynamic reaction travels 'back' (reverse) from the surface to the yoke/rudder.

On many (mostly heavy and/or very fast) aircraft this force link is broken at some point: your muscle force as such doesn't reach the surface, and, more importantly, the reaction doesn't reach you. 'More importantly' because this reaction is the main reason for such arrangement: it is simply too great. So, you don't feel true reaction. This arrangement is called 'irreversible'.
The link is replaced by powered boosters or actuators of some sort, and the reaction is often also recreated (to some comfortable levels) by active or passive means.
Note though that reversible control does not preclude from some automation: the control system may vary the linkage, the autopilot may add its own inputs, trim may change. This may modify the reaction (even down to zero), but in the end there is a hard link, and you can generally feel the changes of force.


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Section alpha and Wing alpha are same or different?
What is the difference between Section alpha and Wing alpha?
Are they the same or different?

What are you talking about? Alpha angle? Please provide a clear context for the question.

More information needed here.

Depends on the reference. The section alpha is for the wing section and measured against the airfoil chord, the connection between the center of the nose radius and the trailing edge.
The wing alpha is measured against an arbitrarily defined reference which might or might not coincide with the section alpha of the wing airfoil. Most wings have washout or airfoil variations over span, so the local section alpha and the wing alpha will coincide at most over some part of the wing only.


text:
What time zone is used for operating an airplane?
This might be a silly question but my thinking was the following:
There has to be a definition of time in an airplane for the logging of data and so on, but what definition would that be assuming a flight goes across timezones?
Would it be the local time at the airport of departure? Or at that of arrival? or maybe even a third, commonly agreed upon time (e.g., GMT)?

The idea came from a story of a friend that was traveling with the ship from Italy (GMT+1) to Greece (GMT+2). The cafeteria on board had a sign saying that it opens at 14:00, but on 14:20 local Italy time, while the ship was anchored in Italy, he was denied service by the crew saying that the sign was referring to Greece local time; where the ship "belongs".

Related, maybe a dupe?

Certainly related. This question asks "what", that one asks "why".  The question of dupe/no dupe could go either way.

Some years ago I had the actual unfortunate (or fortunate depending on perspective) experience of a flight that had a stopover prior to arrival at my location.  All THREE times were for 2:00 AM local - but the FUN part was it was on the day where daylight savings time changed so no-one knew the actual UTC time because of everything being listed in local times.  They just gave me a 4 hour window as best they could do.

There's a huge difference between what's used internally in the computers and what's displayed to customers - what are you asking about?

@pipe Having been a customer myself, I know what is displayed and communicated. I am asking about the pilot-to-plane/ATC interactions, plane internals and so on.

The pilot (and the ATC) use the UTC (Coordinated Universal Time). The flight's departure and arrival are in terms of the local times at the respective airports.
As for data logging, the FDR/CVR usually records in UTC (preferred) or the relative time count (usually count increments each 4 seconds of system operation). See Appendix M to Part 121 - Airplane Flight Recorder Specifications, for example.

The planes use UTC time. The same as ATC.

Thanks for the answer! A link to UTC would be great too (e.g., this)

Let me add that pilots, ATC, and others use UTC, (not GMT) but it's common for customer-facing times to be in the time zone of the event. For example, a Flight from Florida to Alabama may land before it departs on the ticket.
Usually, ticket times are listed in local time. So Departing 1:00 pm Arriving 12:48 pm could actually appear on a ticket.

Well, GMT might mean the same thing as UTC. It is, however, ambiguous.

@coteyr, Please explain how pilots don't use GMT.  If there is a difference between UTC, GMT, and Zulu I would like to understand it.  Thanks.

https://www.timeanddate.com/time/gmt-utc-time.html its mostly semantic but UTC is a system of time where GMT is a time zone.

Zulu, on the other hand, is just shorthand for UTC + 0 Zero hours. For example, a time may be written 20:20z-5:00 (in theory) which is the same at 01:20z


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Airbus Beluga, what is aft of the cockpit?
In the Airbus Beluga (and Beluga XL), the main cargo deck runs the full length of the aircraft, starting just above the cockpit. Is there more usable space behind the cockpit? Or are there fuel tanks here?
In the attached image of a Beluga, there appears to be large door immediatly forwards of the tailnumber, and a smaller door aft.

Image taken from Airbus Beluga promo site

On the Beluga, the area behind the cockpit bulkhead 6 is unpressurized. It contains avionics (A19), the nose wheel and the crew entry hatch (17). It is connected to the forward underfloor cargo bay. That area is unchanged from the A300: it's where the passenger luggage is usually kept. Aft of the wing is another cargo bay.
The same goes for the Beluga XL: underneath the floor, it's identical to a normal A330.

This article indicates the underfloor cargo areas can be used:

... the Beluga XL can carry two A350 wings with additional space for other small components and cargo pallets underneath the main hold floor.
Underneath the freight area is room for 14 LD3 containers as well as a bulk cargo compartment in the far aft.

Thanks, however, I was meaning running the full length behind the cockpit, and below the main cargo deck. According to the sketch you provided, those doors are part 44. These are are labelled "Access doors to cargo bay". I think you called this "the forward underfloor cargo area".  So is this a second cargo bay?